Showing papers by "Geophysical Survey published in 1998"

Simultaneous inversion for velocity structure and hypocenters in Slovenia

Abstract: We use nearly 2100 P-wave arrival times from 166 local earthquakes to investigate the 3-D compressional velocity structure of the upper crust of Slovenia using the simultaneous inversion algorithm developed by (Michelini and McEvilly, 1991). Remarkable and stable features of the resolved model are the relatively high velocities in western Slovenia and the low velocities in central Slovenia, SE of the Ljubljana basin. The boundary between these two anomalies follows approximately the NNW-SSE direction that coincides with the general strike of the External Dinarides. We interpret this feature as the upper crustal expression caused by the tectonic processes occurring along the active margin of the Adria promontory/microplate.

Prestack Kirchhoff depth migration of shallow seismic data

Abstract: Prestack Kirchhoff depth migration is applied successfully to shallow seismic data from a waste disposal site near Arnstadt in Thuringia, Germany. The motivation behind this study was to locate an underground building buried in a waste disposal. The processing sequence of the prestack migration is simplified significantly as compared to standard common (CMP) data processing. It includes only two parts: (1) velocity-depth-model estimation and (2) prestack depth migration. In contrast to conventional CMP stacking, prestack migration does not require a separation of reflections and refractions in the shot data. It still provides an appropriate image. Our data example shows that a superior image can be achieved that would contain not just subtle improvements but a qualitative step forward in resolution and signal-to-noise ratio.

Sewer and pipeline inspection transporter tool

Abstract: A sewer inspection device includes a body that has a number of transducers attached to the body. The transducers are attached on pads that can be extended away from the body to enable the transducers to make contact with a sewer wall. The device is lowered into the sewer in the compact, non-extended position of the pads. Subsequently, the pads are extended to make contact with the sewer walls. The body is pulled along the sewer by means of an armored cable extending to the surface. The armored cable includes a conductor or fiber-optic cable for carrying signals between the transducers and a surface controller. In one embodiment, the transducers generate ground penetrating radar (GPR) signals and detect the reflected signals. Defects in the vicinity of the sewer pipe affect the reflected signals. Analysis of the reflected signals provides information about the nature of the defects. Other embodiments of the invention include sonic, gamma ray and electromagnetic induction transducers. The device may also be provided with a supplementary transducer module on the cable that rests on the bottom of the sewer and makes additional measurements relating to the sewer pipe and its immediate surroundings.